A team of scientists has unearthed the fossil remnants of a tropical forest on the arctic island of Svalbard, and it could help explain one of the most dramatic climate shifts in Earth’s history.

The fossil forest—stumps of lycopod trees that reached heights of about 13 feet—dates back to the late Devonian period some 380 million years ago. (Svalbard, now a frozen wasteland, was a lush chunk of equatorial real estate at that time.) It’s among the oldest forests ever discovered, eclipsed only by a mid-Devonian forest in Gilboa, New York.

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The end of the Devonian was marked by a dramatic global cooling event caused by a drop in atmospheric carbon dioxide levels. One explanation for the atmospheric shift is the rise of CO2-hungry forests, but to date, very few Devonian trees have actually been found. Firm evidence for tropical forests at the end Devonian supports the theory that trees had a big role to play in the climactic shift that would usher in an era of complex terrestrial ecosystems.

“During the Devonian Period, it is widely believed that there was a huge drop in the level of carbon dioxide in the atmosphere, from 15 times the present amount to something approaching current levels,” said Cardiff University’s Chris Berry, lead author on a study appearing this week in Geology.

“The evolution of tree-sized vegetation is the most likely cause of this dramatic drop in carbon dioxide because the plants were absorbing carbon dioxide through photosynthesis to build their tissues, and also through the process of forming soils,” he continued.

Ultimately, Devonian trees probably set the stage of land-based life as we know it. It’s a nice reminder that plants were engineering the Earth long before humans came on the scene—and that we owe our very existence to their efforts.